The present invention relates to a process for producing molten metal (which term includes metal alloys), in particular, although by no means exclusively iron, from a metalliferous feed material, such as ores, partly reduced ores and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a process and an apparatus for producing molten metal from a metalliferous feed material which is based on the combination of:
(a) a means which partially reduces and at least partially melts the metalliferous feed material; and
(b) a means which completes reduction of the molten partially-reduced feed material.
One example of a pre-reduction/melting means is a cyclone converter.
One example of a reduction means is a vessel that contains a molten bath.
U.S. Pat. No. 4,849,015 of Fassbinder et al and U.S. Pat. No. 5,800,592 of Den Hartog et al disclose particular proposals for producing molten iron from iron ore using the above combination of pre-reduction/melting means and reduction means.
One object of the present invention is to provide an alternative process/apparatus for producing molten iron from iron ore which is based on the above combination of pre-reduction/melting means and reduction means.
According to the present invention there is provided a process for producing metals from a metalliferous feed material which includes the steps of partially reducing and at least partially melting the metalliferous feed material in a pre-reduction/melting means and completely reducing the partially reduced feed material in a reduction means, which reduction means includes a vessel that contains a molten bath having a metal layer and a slag layer on the metal layer, and which process is characterised by:
(a) injecting solid carbonaceous material with a carrier gas into a metal rich region of the molten bath;
(b) causing upward movement of splashes, droplets, and streams of material from the metal layer which:
(i) promotes mixing of material from the metal layer in the slag layer and mixing of material from the slag layer in the metal layer; and
(ii) extends into a space above the molten bath to form a transition zone;
(c) injecting an oxygen-containing gas into the vessel and post-combusting part of a reaction gas generated in the molten bath;
(d) transferring at least part of the hot reaction gas from the reduction means to the pre-reduction/melting means as a reducing gas and partially reducing the metalliferous feed material; and
(e) injecting an oxygen-containing gas into the pre-reduction/melting means and post-combusting a part of the reaction gas and thereby generating heat which at least partially melts the partially-reduced metalliferous feed material.
The term xe2x80x9cmetal rich regionxe2x80x9d is understood herein to mean the region (or regions) of the molten bath that has a high concentration of metal. By way of example, the metal layer is one metal rich region.
The term xe2x80x9cmetal layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly metal. Specifically, the term covers a region or zone that includes a dispersion of molten slag in a metal continuous volume.
The term xe2x80x9cslag layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly slag. Specifically, the term covers a region or zone that includes a dispersion of molten metal in a slag continuous volume.
The term xe2x80x9ctransition zonexe2x80x9d is understood herein to mean a gas continuous volume with splashes, droplets, and streams of molten material (which is at least predominantly slag) therein.
One option for generating the upward movement of splashes, droplets and streams of molten material from the metal layer in step (b) is to inject the solid carbonaceous material and carrier gas in step (b) via one or more than one lance/tuyere that extend downwards towards the metal layer.
More preferably the one or more than one lance/tuyere extend through side walls of the vessel and are angled inwardly and downwardly towards the metal layer.
It is preferred that the injection of solid carbonaceous material and carrier gas into the metal layer be sufficient to generate upward movement of splashes, droplets and streams of molten material in a fountain-like manner.
The injection of solid carbonaceous material and carrier gas into the metal layer via the downwardly extending lance(s)/tuyere(s) has the following consequences:
(i) the momentum of the solid carbonaceous material/carrier gas causes the solid carbonaceous material and gas to penetrate the metal layer;
(ii) the solid carbonaceous material, typically coal, is devolatilised and thereby produces gas in the metal layer;
(iii)carbon predominantly dissolves into the metal and partially remains as solid;
(iv) the gases transported into the metal layer and generated via devolatilisation produce significant buoyancy uplift of material from the metal layer which results in the above-described upward movement of splashes, droplets and streams of material, and these splashes, droplets, and streams entrain further slag as they move through the slag layer.
The material referred to in paragraph (d) includes molten metal (which includes dissolved carbon) and molten slag that is drawn into the metal layer from above the metal layer as a consequence of solid/gas injection.
Another option, although by no means not the only other option, to generate the above-described upward movement of splashes, droplets, and streams of material is to inject solid carbonaceous material and carrier gas via one or more than one tuyere in the bottom of the vessel or in side walls of the vessel that contact the metal layer.
Preferably, the pre-reduction/melting means is positioned above the reduction means and communicates with the reduction means so that at least partially molten, partially reduced metalliferous feed material drains downwardly into the reduction means and, more particularly, drains into the vigorously mixed central region of the slag layer in the molten bath. The applicant believes that this leads to more efficient smelting of the pre-reduced material.
Preferably with this arrangement hot reaction gas generated in the reduction means flows upwardly into the pre-reduction/melting means.
As indicated above, the upward movement of splashes, droplets and streams of material from the metal layer promotes mixing of material from the metal layer in the slag layer and mixing of material in the slag layer in the metal layer. Preferably, the extent of mixing is sufficient so that the slag layer is more or less homogeneous in terms of composition and temperature.
The mixing of material between the layers promotes reduction of metal oxides present in the molten bath by dissolved carbon in metal. In this connection the injection of solid carbonaceous material into the metal layer ensures that there are high levels of dissolved carbon (and possibly solid carbon) in the metal layer and that, as a consequence, the metal layer is strongly reducing.
It is preferred that the level of dissolved carbon in metal be greater than 3.5 wt %.
Preferably the process includes the step of preheating the metalliferous feed material before supplying the metalliferous feed material into the pre-reduction/melting means.
Preferably the process includes discharging reaction gas from the pre-reduction/melting means as an off-gas and preheating the metalliferous feed material with the off-gas, either hot or cold.
Preferably steps (c) and (e) of injecting the oxygen-containing gas into the vessel and the pre-reduction/melting means post-combust the reaction gas generated in the molten bath to a post-combustion level of at least 70%.
The term xe2x80x9cpost-combustionxe2x80x9d means:             [              CO        2            ]        +          [                        H          2                ⁢        O            ]                  [              CO        2            ]        +          [                        H          2                ⁢        O            ]        +          [      CO      ]        +          [              H        2            ]      
where:
[CO2]=volume % of CO2 in the reaction gas;
[H2O]=volume % of H2O in the reaction gas;
[CO]=volume % of CO in the reaction gas; and
[H2]volume % of H2 in the reaction gas.
More particularly, the term xe2x80x9cpost-combustionxe2x80x9d in the context of post-combustion in the vessel also means post-combustion in the absence of any addition of supplementary carbonaceous material for other purposes.
Preferably injection of oxygen-containing gas into the vessel in step (c) is via one or more than one lance/tuyere that extend downwardly and inwardly into the vessel and are set back sufficiently to be clear of material flowing downwardly from the pre-reduction/melting means into the vessel.
The transition zone is important for three reasons.
Firstly, the ascending and thereafter descending splashes, droplets and streams of material are an effective means of transferring to the molten bath the heat generated by post-combustion of reaction gas in the vessel.
Secondly, the material, and particularly the molten slag, in the transition zone is an effective means of minimising heat loss by radiation via the side walls of the vessel.
Thirdly, dust containing carbon in the transition zone reduces heat loss by radiation to the side walls of the vessel.
Preferably, the vessel includes:
(a) tap holes for discharging molten metal and slag from the vessel; and
(b) one or more than one outlet for transferring reaction gas to the pre-reducing/melting means.
It is preferred that the oxygen-containing gas be oxygen.
According to the present invention there is also provided an apparatus for carrying out the above-described process.
More particularly the present invention provides an apparatus for producing metals from a metalliferous feed material which includes: a pre-reduction/melting means which partially reduces and at least partially melts the metalliferous feed material and a reduction means which completely melts and reduces the at least partially molten and partially reduced feed material; which reduction means includes a vessel that contains a molten bath having a metal layer and a slag layer on the metal layer; which pre-reduction/melting means is positioned directly above the vessel and communicates with the vessel whereby at least partially molten and partially reduced feed material flows downwardly into a central region of the vessel; and which reduction means further includes:
(a) one or more than one lance/tuyere which inject solid carbonaceous material with a carrier gas into a metal rich region of the molten bath;
(b) one or more than one lance/tuyere which inject oxygen-containing gas into the vessel that post-combusts reaction gas generated in the vessel, the one or more than one lance/tuyere extending downwardly and inwardly into the vessel and being positioned so as to minimise contact with at least partially molten and partially reduced feed material flowing downwardly from the pre-reduction/melting means; and
(c) one or more than one lance/tuyere which inject oxygen-containing gas into the pre-reduction/melting means that post-combusts at least a part of the reaction gas from the vessel.